ROverloading

[John Max Skaller <skaller@ozemail.com.au>]

Mattias Waldau wrote:

> >> I would like to note that type inference (i.e. code without
> >> annotations) helps a lot when developing programs: the annotation free
> >> code is not only easier to write but also easier to maintain since it
> >> is kind of ``auto-adaptative'' and resistant to reorganisations and
> >> names modifications.
> 
> If this were important, we shouldn't have different operators for * and *.
> I had to change a program from integers to float recently, and it isn't fun
> at all.

	Overloading is, perhaps unfortunately, more or less
mandatory in the long run, perhaps not so much to support 'ad hoc
polymorphism'
as to relieve the programmer of learning lots of names for
things. In Ocaml, learning + for int and +. for float isn't
so bad. But add in ten other integer representations, and we're rapidly
forced to resort to named prefix operators (i.e. function names).

	Unfortunately, overloading isn't quite so simple when 
you've also got type inference:

	let f a b = a + b in
	let x = f 1.0 2.0 in
	let y = f 1 2 in 

If we take 'f' to be monomorphic, then
the second call is in error, because the overloaded + in the
definition of 'f' doesn't determine it's type until x is
calculated. Otherwise, 'f' could be taken to define an overloaded
set of functions (somewhat like a C++ template) and the calculations
of x and y would call different specialisations .. but this rapidly
gets quite messy.

Felix supports overloading, but it works more easily because
functions must be explicitly typed. Nevertheless it is sometimes
necessary to explicitly resolve an overload:

	function f(a:int):int { ..}
	function f(a:float):float { ..}
	val g = f of (int); // which f?

because there is inference of val's and var's, and, even without that:

	function g(f:int->int):int { .. }
	function g(f:float->float):float { .. }
	.. g(f of (int)) .. //which g? depends on which f!


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John (Max) Skaller, mailto:skaller@maxtal.com.au
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